1. Field of the Invention
The invention relates to a process for preparing isocyanatoorganosilane.
2. Description of the Related Art
For some time there has been great interest in an economic method for preparing isocyanoatoorganosilanes in high yields and purities. Said compounds are of great economic importance since they are used, for example, industrially as adhesion promoters between organic polymers and inorganic materials (also termed coupling agents, crosslinkers).
For their preparation, processes are preferred in which the starting materials are almost completely safe or completely safe in order to facilitate handling and procedure. In the case of the processes previously used, however, isocyanoatoorganosilanes are prepared in relatively low amounts, and in low-efficiency and expensive processes.
For instance, in the process described in U.S. Pat. No. 6,008,396, carbamatoorganosilanes are converted in inert hot media to the isocyanates, with elimination of alcohol. However, this process can only be operated semi-continuously, since the concentration of impurities in the medium, even after a short time, increases in such a manner that the desired purity of the product is no longer ensured.
In the process described in U.S. Pat. No. 3,598,852, carbamatoorganosilanes are vaporized in vacuum and the isocyanatosilane formed is distilled off continuously.
In the process described in EP 1010704 A2 carbamatoorganosilanes are thermally cleaved in the liquid phase to give the corresponding isocyanoatoorganosilanes with catalysis by Sn(II) chloride. Particularly the highly complex process for isolating and purifying the desired products which leads to low yields has been found disadvantageous in this process, and thus it appears not to be of interest for application on an industrial scale.
EP 649850 B1 discloses the thermal cleavage (thermolysis) of carbamatoorganosilanes in the gas phase at atmospheric or reduced pressure. However, the yields obtainable by this process, in particular of isocyanatomethylorganosilanes, are unsatisfactory under the conditions described there.